The invention relates to a method and apparatus for sensing the temperature of a fluid utilizing a transmitting and receiving transducer (such as piezolectric material which converts electrical pulses to pulses of ultrasonic energy and vice-versa) for emitting and receiving sound pulses. While the invention has applicability for the sensing of the temperature of the surrounding fluid in a wide variety of environments, the invention is particularly useful in association with a system for monitoring the level of liquid within a liquid holding tank, such as the amount of gasoline in a gasoline tank at a service station or the like. It has been found that an ultrasonic transducer is eminently suited for liquid level monitoring, and according to the invention the same transducer utilized to monitor the liquid level can be utilized to determine the temperature of the liquid.
For the particular application where the invention is utilized with a liquid level monitoring system, a number of functional advantages result. Gasoline, and other liquids, of course, expand and contract with temperature, and for large storage tanks such an expansion and contraction can result in a considerable change in the volume of gasoline within the tank. The gasoline tank monitoring systems commonly used desirably are useful in detecting leaks of gasoline from the tank. So that such systems do not falsely indicate leakage of gasoline due to contraction as a result of temperature changes, it is necessary to determine the temperature of the gasoline and to compensate for the temperature in determining the amount of gasoline within the tank. Then a true value of the amount of gasoline within the tank can be determined. The invention can also be used to verify that the amount of gasoline to be delivered to the tank has been delivered.
According to a specific aspect of the present invention, a method of determining the volume of gasoline (or other liquid) in a tank is provided. The method is practiced utilizing a transmitting and receiving transducer for emitting and receiving sound pulses, and a movable target. The method comprises the steps of: Disposing the transducer and movable target in the liquid within the tank so that sonic pulses emitted by the transducer impact upon, and are reflected by, the movable target and pass through the air-liquid interface. Mounting the movable target so that it moves in response to temperature of the liquid in a known manner with respect to the transducer. Emitting sound pulses from the transducer so that they reflect off the movable target and reflect back from the air-liquid interface; and, using the reflected sound pulses received by the transducer to determine the level of liquid within the tank, and the density of the liquid as related to the temperature of the liquid, to thereby calculate the amount of liquid within the tank.
According to a more general method within the scope of the present invention, a method of sensing temperature of a fluid is provided. The method utilizes a transducer and a movable target. The method comprises the steps of: Disposing the transducer and movable target within the fluid or liquid whose temperature is to be sensed. Mounting the movable target with respect to the transducer so that the target moves in response to temperature changes in the fluid in a known manner with respect to the transducer; and, emitting and receiving sound pulses with the transducer so that the sound pulses reflect off of the target and back to the transducer to thereby allow calculation of the distance of the moveable target from the transducer, and thus the temperature of the fluid. The method also preferably comprises the step of calibrating the transducer (for instance so that it is not affected by differences in the particular properties of the fluid) by providing a second stationary target for the transducer, mounted a fixed known distance from the transducer.
The fluid temperature sensing apparatus according to the present invention comprises the following elements: (a) Transmitting and receiving transducer means for emitting and receiving sound pulses. (b) A first target for reflecting sound pulses emitted by the transducer means. (c) Temperature responsive means affixed to the first target for moving the target in a known manner in response to temperature changes in the fluid. The temperature responsive means preferably comprises a coil of bimetallic material stationarily mounted on one end thereof with respect to the transducer, and having a lever at the other end thereof, the lever affixed to the target, which may comprise a stainless steel generally cylindrical member. And, (d) means for mounting the temperature responsive means in operative association with the transducer means so that the target moves toward and away from the transducer means in a known manner in response to changes in temperature in the fluid. The mounting means preferably comprises a tube of rigid material (such as fiberglass), with the transducer mounted within the tube, and with the coil mounted to the tube so that the first target is within the tube. Also, to effect calibration of the system, a second, stationary target preferably is provided. The second target is mounted to the tube so that it is within the tube and is spaced a fixed, known distance from the transducer.
The invention also comprises the abovementioned components mounted so that the tube is at the bottom of a liquid (e.g. gasoline) holding tank so that sound pulses emitted from and received by the transducer pass to and from the air-liquid interface within the tank. The information received by the transducer from the movable and stationary targets, and from the air-liquid interface, is utilized by a microcomputer to determine the amount of liquid within the tank.
It is the primary object of the present invention to provide a simple and effective mechanism and procedure for determining the temperature of a fluid, which is particularly useful in determining the amount of liquid in a liquid holding tank. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.